1. Field of the Invention
The present invention relates to a multimedia optical disc which stores multimedia data including digital video data, audio data and sub-picture data as well as to a reproducing device for the disc. More specifically, the invention is a technique for the easy realization of branch reproduction to parental lock sections using reduced control information.
2. Description of the Related Art
In recent years there has been an increase in the use of optical discs, such as laser discs and video CDs, as optical storage media for recording multimedia data made up of video, audio and other such data.
Of these, video CDs have achieved a storage capacity of around 600 MB (megabytes) for a medium which was originally used for digital audio, with the storage of video data having been achieved due to the development of a high-compression video data compression method called MPEG (Moving Pictures Experts Group). In this way, movie titles which were stored on laser discs can now be stored on video CDs.
As the result of recent research and development, DVDs (digital video discs) which achieve a dramatic increase in storage capacity have been developed. Such DVDs have a storage capacity of around 4.7 GB (gigabytes), so that video whose image quality is vastly superior to video CDs (whereby an increased amount of data is used per unit reproduction time) can be stored and the maximum reproduction time can be increased to allow the recording of long titles. More precisely, the reproduction time of 74 minutes which is possible with a video CD can be increased to over two hours for a DVD. For these reasons, DVDs allow the storage of movies which, due to their long reproduction time, cannot be recorded on video CDs, with the long reproduction time and high picture quality making DVDs ideal for such storage.
Regarding movie titles, it is quite common for several different versions of a same movie to exist, such versions differing from each other in content. As examples, there can be an adult version and a general viewing version, a cut version and a no-cut version, or a cinema version and a television broadcast version.
The following is an explanation of a first conventional reproduction system for reproducing a specified version out of a plurality of different versions of a same movie which are efficiently stored on an optical disc.
This reproduction system includes a registering unit, a selecting unit and a reading unit and is a system which selects and reproduces one out of two or more versions of a same film stored on a software carrier.
The software carrier referred to here has the video data blocks of the following three types stored on a same track.
1. Blocks including video data unique to one of the two or more versions. PA1 2. Blocks including video data unique to another of the two or more versions. PA1 3. Blocks including video data which is common to two or more versions. PA1 a comparing unit for comparing the level information registered in the registering unit and level identifiers in the management information stored on the optical disc; PA1 a first determining unit for determining, when a comparing result of the comparing unit is that there is a level identifier which matches the level information, a video data sequence which has the matching level identifier; and PA1 a second determining unit for determining, when a comparing result of the comparing unit is that there is no level identifier which matches the level information, a video data sequence which has a level identifier which is closest to the level information but which represents a more restricted content of a video data sequence.
For this kind of reproduction system, the registering unit registers which of the versions is to be reproduced. The selecting unit selects the common blocks and only the blocks which are unique to the selected version. The reading unit reads the video data for the selected blocks from the software carrier and generates a reproduction signal, with the video data in the same track which is unique to a version which is not being played being excluded.
FIG. 1 shows the aspects of reproduction of a plurality of video data blocks by such a conventional reproduction system. In this drawing, optional block A is video data unique to version A (such as an adult version), optional block B is video data unique to version B (such as a general viewing version) and common blocks 1 and 2 are video data which is common to both versions.
In the present example, the blocks described above are recorded on a software carrier and "version B" is registered in the registering unit of the reproduction system. In this case, common block 1, optional block B and common block 2 are selected in that order by the selecting unit and the video data in common block 1, optional block B and common block 2 is read by the reading unit.
By means of this kind of conventional system, for an example when an adult and a general viewing version of a same movie title are recorded on a software carrier, the continuous reproduction of only the general viewing version or only the adult version can be achieved. By doing so, a parental lock can be achieved whereby parents can ensure that the reproduction of a general viewing version, which does not include scenes featuring sex or violence that are unsuitable for minors, is performed.
Here, while the conventional system described above can achieve the continuous reproduction of one version, it is totally unsuited to the reproduction of interactive applications where interaction between the user and the system is possible.
Interactive movies, which have been paid a lot of attention in recent years, provide one example of such an interactive application. Here, "interactive movies" refers to movies where the story develops in accordance with selections made by the viewers. As one example, there can be completely different developments in the story depending on a choice made by the viewers at a given scene, such as the story developing so that the leading character goes from country A to country B via a third country, or alternatively, the story developing so that the leading character goes straight from country A to country B.
FIG. 2 is a drawing for showing an example of the reproduction paths which are necessary for an interactive application. As one example, the four blocks in this drawing show the versions A and B for a story wherein the leading character goes from country A to country B via a third country.
For these two versions, the decision of whether or not the leading character visits the third country before visiting country B is made according to a viewer selection. In order for the story to develop so that the leading character can go straight to country B, it is necessary to introduce a shortcut, as shown by the dotted line in FIG. 2, to skip the scenes where the character visits the third country. By making such a shortcut, the reproduction can be such that the scene where the leading character arrives in country B can be shown after the reproduction has followed the story in common block 1 up to the departure from country A. For a conventional reproduction system, the realization of this kind of interactive branch reproduction to a parental lock section has been extremely problematic.
In order to achieve the above reproduction using the stated conventional technique, it would be necessary to use a plurality of branch instructions as described below as the reproduction control information. One of these branch instructions informs the reproduction system of a branch to the reproduction position for the scene depicting arrival in country B in unique block A when version A is being reproduced while another of these branch instruction informs the reproduction device of a branch to the reproduction position for the scene depicting arrival in country B in unique block B when version B is being reproduced. This is to say, a same number of branch instructions as there are unique blocks (versions) become necessary just to realize one shortcut.
In general, for an interactive movie, the greater the amount of story branches, the greater the viewer's sense of wonder at the variety of story developments. In order to achieve this, it is necessary to have branch instructions for each of the different story developments from the branching points of the story. Since these branch instructions need to be stored in the memory of the reproduction system before the reproduction of the video data in the block, the memory capacity of such reproduction system needs to be greater, the more such branch instructions are present.
In particular, when there are a plurality of such branching points in the video data, it becomes necessary to store an extremely large number of branch instructions in the memory. For the previous example of a shortcut from country A to country B, suppose that there are ten different branching points provided for common block A, which can represent an opportunity for the character to travel by car, an opportunity for the character to travel by airplane, an opportunity for the character to travel by train and the like. In this situation, it becomes necessary to store all of the branch instructions which can be executed at these opportunities in the memory of the reproduction device.
The problem of this increase in the necessary memory size of the reproduction device becomes especially severe for interactive applications which include parental lock sections as described above. This is because when a branch is performed to a parental lock section, separate branch instructions are necessary for each of the levels in the parental lock section. As one example, if it is supposed that at one reproduction position of an interactive movie there are N possible branches which each represent a different development in the story and, for each branch address, separate blocks on M different levels (versions) for viewing control of the sex scenes or violent scenes present in the video data, a total of N*M branch instructions would need to be set for this reproduction position. Furthermore, if there are L branching points in a video data block, a total of N*M*L branch instructions need to be stored beforehand in the memory in order to reproduce this video data block. Accordingly, a memory of substantial storage capacity becomes necessary for the reproduction device.
Here, it is desirable to restrict the memory capacity of the reproduction device to a minimum. This is because by doing so, the reproduction device can be supplied at a lower price to the consumer. This is also true for other consumer AV equipment such as video CDs and laser discs where the memory capacity is suppressed to a minimum in order for makers to provide the equipment at an affordable price. As a result, the above method which requires a great number of branch instructions to be stored in a memory is not economically viable for such conventional consumer AV equipment.
In this way, for conventional systems it has been very difficult to achieve interactive reproduction control where reproduction control is performed to selectively reproduce parental lock sections when there is heavy use of branch reproduction.